1) Field of the Invention
The present invention relates to an image forming apparatus, like a copying machine, a facsimile, and a printer, that forms an image by an electrostatic copying process. More particularly, the present invention relates to an image forming apparatus that includes a cleaning unit that cleans toner remaining on an image carrier.
2) Description of the Related Art
A charge is applied on a surface of an image carrier in an electrophotographic copying machine and the surface is exposed to thereby form an electrostatic latent image on the surface. A developing unit spreads toner on the surface to thereby develop the image. A transferring unit then transfers the image to a recording medium like a paper. A cleaning unit removes the excess toner (hereinafter, “residual toner”) that remains on the surface of the image carrier.
The residual toner may be removed with a rotating brush, with a cleaning blade, or with suction. The cleaning blade has been used widely as it has a simple structure and high efficiency. The cleaning blade is made of an elastic material that includes rubber like urethane elastomer. The urethane elastomer scrapes the image carrier and removes the residual toner on the surface of the image carrier.
However, when the surface of the image carrier is scraped, frictional force is developed between the cleaning blade and the image carrier. Particularly, since an edge of the cleaning blade and the surface of the image carrier are uneven, and moreover, due to presence of foreign matters like toner that is fused, external additive that is separated, paper dust, the cleaning blade vibrates. As a result, a gap is developed between the cleaning blade and the image carrier that causes improper cleaning.
Since a highly accurate image recorded by the image forming apparatus is sought these days, there is a tendency to reduce particle size of toner and to make the toner particles round. If the particle size of toner is small, greater amount of force is required for removing the residual toner on the image carrier by cleaning, and a cleaning unit cannot clean the image carrier properly. If the toner is made round, the toner particles tend to enter between the cleaning blade and the image carrier and the cleaning unit cannot clean the image carrier properly.
To solve the problems, a cleaning blade having improved efficiency is disclosed in Japanese Patent Application Laid-open Publication No. H9-218624. In this cleaning blade, polysiloxane oil having a molecular structure that has at least one reactive part at one terminal is included in the polyurethane elastomer. As a result, it is possible to provide the cleaning blade without bending and stick-slip due to low friction, at a low cost.
A cleaning unit in which the noise due to the vibration of a cleaning blade that scrapes the residual toner on the image carrier after transferring an image, is eliminated, is disclosed in Japanese Patent Application Laid-open Publication No. H5-107994. In the cleaning unit, the cleaning blade that is in pressurized contact with the image carrier is made of a material that has impact resilience in a range of 40 percent to 60 percent at 25° C. As a result, the resonance due to the vibrations of the cleaning blade is eliminated.
An image forming apparatus in which an image with a high quality and durability can be achieved by eliminating problems such as coming off of toner, fusion of toner on surface of the image carrier, noise, abnormal vibrations, and bending of blade, is disclosed in Japanese Patent Application Laid-open Publication No. H11-174922. The image forming apparatus is equipped with a piezoelectric element (vibrations applying unit) that applies vibrations to the cleaning blade. As a result of this, problems such as coming off of toner etc. are eliminated.
However, the cleaning blade, the cleaning unit, and the image forming apparatus disclosed in these patent documents have not been able to control the slipping of toner from the cleaning blade in an environment where the image forming apparatus is to be used, thereby causing improper cleaning. Moreover, the cleaning blade, the cleaning unit, and the image forming apparatus have not been able to prevent improper cleaning in an image forming apparatus that use a round shaped toner having a small particle size.